Answer:
Option D, A radula
Step-by-step explanation:
Complete question
Which structure do sea slugs use to feed on their prey?
A) nematocysts
B) a sharp beak
C) an incurrent siphon
D) a radula
E) a mantle cavity
Solution
Sea slung are known as marine gastropod mollusks and like all other member of the mollusk family, sea slug uses their radula to capture their food.
A radula is basically a chitinous ribbion which is used for holding, cutting and chewing food.
Most of the gastropod mollusks feed on diatoms by grazing and scraping them through radula.
Hence, option D is correct